Method of producing coated glass articles



Jan. 30, 1962 L. E. ORR 3,019,135

METHOD OF PRODUCING COATED GLASS ARTICLES Original Filed May 19, 1955 2Sheets-Sheet 1 INVENTOR LEIGHTU/Y 5. m0

Jan. 30, 1962 L. E. ORR

METHOD OF PRODUCING COATED GLASS ARTICLES 2 Sheets-Sheet 2 OriginalFiled May 19, 1955 INVENTOR LE/GHTON E. can

6 TTOI'FNE Y United States Patent Ofiiice 3,019,135 Patented Jan. 30,1962 17 fl'lairns. (Q1. 117-211) The present application is a divisionof application Serial No. 509,552, filed May 19, 1955, for Method ofProducing Coated Glass Articles, which in turn, is copending withapplication Serial No. 220,429 of Leighton E. Orr, filed April 11, 1951for Method of Producing an Electroconductive Article, now abandoned,which in turn, is a continuation-in-part of application Serial No.61,191, filed November 20, 1948, now U.S. Patent No. 2,569,773.

This invention relates to an improved method for depositing non-uniformcoatings upon ceramic or refractory viewing closures. In one aspect, thepresent invention relates to depositing electroconductive transparentcoatings upon ceramic or refractory viewing closures, particularly thoseprovided with laterally spaced electroconductive strips or bus bars inelectrical contact with the film and adapted to facilitate passage ofelectric current through the coating.

According to the present invention, conventional methods hitherto usedto produce metal oxide films, wherein a relatively cool spray of filmforming composition capable of forming a metal oxide film uponcontacting a refractory base whose temperature is above 400 F., butincapable of forming a metal oxide film upon contacting the refractorybase when the base is at a temperature substantially below 400 F. isapplied to a previously heated refractory base, are modified accordingto the teaching of the present invention to produce metal oxide films ofvarying thickness. Specifically, a sheet of refractory material isheated in a furnace above film forming temperature and below thetemperature at which the base becomes molten, removed from the furnacein proper orientation relative to the spray, and immediately exposed toa spray of a film forming composition having at least one dense and onesparse region. Relative motion is established between the base and thespray at such a velocity that a continuous film having a transversethickness pattern conforming to the spray density pattern forms on thebase. However, since the realization that each increment of the basealong the axis of relative movement is cooled upon contact with thespray, it has been found necessary, according to the present invention,to remove each increment from contact with the spray before thetemperature of any portion of the increment falls below the minimum filmforming temperature. Failure to effect this removal in time results in atendency of the film to depart from its variation transversely of theaxis of movement and become more uniform in thickness.

It is known that transparent electroconductive films may be depositedupon glass by applying stannic chloride to the surface of glass heatedabove 400" F., preferably 850 to 1350 F. Films of superior conductivitymay be produced by spraying plate, window or other glass while it isheated to a temperature of above 400 F. but below the temperature atwhich the glass becomes molten, with tin tetrachloride or other tinsalts in aqueous solution or in vapor state, in the presence of areducing agent such as methanol, phenyl hydrazine hydrochloride, orother agents. The films thus obtained are of unknown composition, butappear to contain a preponderant amount, on the order of 97% to 99%, ofa tin oxide and certain impurities which may include metallic tin,carbon, silicon, sodium and chlorine and other impurities, dependingupon the composition of the applied tin containing solution. These filmshave a thickness of about 50 to 800 millimicrons, are transparent andhave the unusual characteristic of being electroconductive. Theparticular degree of electroconductivity is dependent, to a largedegree, upon the nature of the process of depositing the films and thecomposition of the tin bearing solution. These tin oxide films have asurface resistivity below about 500 ohms per unit square, and a specificresistivity below about 0.01 ohm centimeters. Further details respectingthe production of these films will be supplied hereinafter.

Although articles having such films are useful in many fields, they havebeen found to be especially useful as Windshields or viewing closures inautomobiles, aircraft, trains and similar motive vehicles. In such use,the coating is placed in series with a source of electric potential andis used as a heating element in order to heat the closure and preventdeposition of ice, fog, etc. thereupon.

In the production of such electroconductive articles, a glass sheet,usually of plate glass or other flat glass structure (including bent orcurved glass structures), is provided with conducting metal stripssuitable for bus bars. These strips are generally located adjacent theedges of the glass (usually within 0.5 inch of the edge) and, in thepreferred embodiments, are located on opposed marginal edges. Forexample, in an essentially rectangular viewing closure such as awindshield, two bus bars are applied on a pair of opposite marginaledges.- These metallized strips must be capable of withstanding thetemperatures and oxidizing conditions of treatment and, therefore,preferably should be of a ceramic character. Furthermore, they should becapable of glazing or otherwise forming an adherent, well-bonded coatingto the glass. The strips should adhere firmly to the glass sheet, andshould have a conductivity at least 10 to 20 times that of theconductive coating. Generally, the strips are from about 0.1 to 1 inchin width. Also, strips of an air drying non-fired silver may be placedatop the electroconductive coating for the bus bars.

In practice, it has been found that the most satisfactory compositions,for use in preparing the bus bars, comprise a highly conductive metalpowder (preferably gold or silver), and a vitrifying binder. Theingredients forming the vitrifying binder, for example, litharge, boricacid and silica, are heated to a sufficient temperature, for example1700 F., to compel them to fuse and form a glassdike mass. This mass isthen converted into a frit by grinding, usually in a ball mill. Theelectroconductive metal, such as finely divided silver, is then added tothis frit and spraying or screening vehicles are added to thecompositions to facilitate their application. Some of the vehiclesusually employed are French fat oil, turpentine, water and ethylalcohol. In order to avoid production of bus bars which will develop, inuse, excessive stresses in the glass, the bus bars preferably should belocated on the extreme edge of the glass and the bus bar thicknessshould not exceed about 0.005 inch and, preferably, should be belowabout 0.003 inch.

After application of the metal bus bars to the glass sheet by paintingor other method, the sheet is heated to the temperature at whichapplication of the conductive coating may be effected, for example,above about 400 to 800 F. but below the fusion point of the glass.Usually,

950 to 1150" F. is the temperature range selected. Dur-.

ing this heating operation, the ceramic metal coating becomes glazed andis fused onto the glass so that a firm bond is established between theglass and the metal coating.

When the glass has been heated as described above, for two or moreminutes, it is withdrawn from the heating chamber and immediatelysprayed with the coating solution before substantial cooling of theglass sheet can take place. A quantity of the coating solution is placedin an atomizing spray gun and the heated glass sheet is sprayed with anatomized spray of this material. Usually this spraying operation isconducted in air of atmospheric humidity or oxygen. However, conductivecoatings have been obtained even when oxygen appears to be absent,although it is probable that oxygen, either from the atmosphere orcombined in water or similar compound, is present. This process resultsin the production of a base coated with a tin oxide electroconductivefilm.

Articles produced according to the above description, further details ofwhich will be supplied below, are suitable for use as viewing closuresor windows. Usually they are laminated with a suitable plastic Such aspolyvinyl butyral to reinforce the glass and provide a so-called safetyglass construction. These closures may be heated successfully byimposing an electric potential across the bus bars, thus using theconductive film as a resistance element.

Products so made have been satisfactory where the energy requirementsfor heating the glass sheet have not been large. In many cases, however,these products must be capable of supplying quite large amounts of heat,for example above 1500 to 2000 B.t.u. per hour per square foot. Suchrequirements mean that electric currents of substantial amperage passthrough the film.

It has been found that an unduly large number of windshields or likepanels of the type herein contemplated have failed in use or in testbecause of glass fracture during passage of current through theelectroconductive film. The present invention may be utilized tomanufacture articles less subject to failure. This is accomplished byapplying eleetroconductive films having non-uniform resistance'per unitarea. The distribution of the surface resistivity of the film so appliedin such that areas in the film which tend to develop the highesttemperature and/ or to generate the most heat are located at pointsspaced from the bus bars a substantial distance, for example at least 5to of this distance between the bus bars. This is usually at least 1 to2 inches for commercial windshields. This may be accomplished byproviding electroconductive films which have their maximum conductivityimmediately adjacent the bus bar and lower conductivity in the areaspaced from the bus bars in the current path between bus bars.

Ideally speaking, it is desirable that each area or areas of maximumheat generation or temperature development be spaced from the bus barsas herein contemplated. However this may not be entirely possiblebecause of the configuration of the sheet or base.

For example, many articles having electroconductive films are notrectangular. Consequently, bus bars near opposite edges thereof may beof unequal length and may be disposed in a non-parallel manner.Frequently, in such cases, high current densities tend to be establishedat the ends of the bus bars particularly when the bus bars are taperedto a point at their ends. Similarly, the distance between opposed partsof the bus bars may vary so greatly as to establish high currentdensities at certain areas along a bus bar. At these areas, heatgeneration tends to be high and may even exceed the heat generation ofother areas on the sheet or base. This is undesirable and should beavoided.

Even in cases where it is impossible or exceedingly difficult to avoidsome hot spots at or near the bus bar, the amount of heat generationand/or temperature in crease may be reduced by providing a film area inthe current path to such hot spots having higher resistance per unitsquare than that of the film adjacent the bus bar.

The provision of films wherein the preponderant areas of maximumresistance per unit area are spaced a substantial distance from the busbars offers certain advantages in addition to minimizing breakage andbreakdown of the film adjacent the bus bars. When articles hereincontemplated are used as viewing closures in aircraft or other vehicles,the central area of the film remains free of ice, snow or mist underatmospheric conditions so severe that it is not possible with the poweravailable to prevent their accumulation over the entire panel surface.

It has been found that when stannic chloride or like film formingcompound is sprayed upon a hot glass surface even for a relatively shortperiod of time during which the surface is cooled to below film formingtemperature, the resulting transparent film is essentially uniform inthickness even though the density of the spray is not uniform. Accordingto this invention, however, it has been discovered when a spray ofnon-uniform density is used, a film of non-uniform thickness may beobtained if the spraying operation is interrupted early enough andbefore essentially uniform film thickness has been achieved.

Thus, in accordance with this invention, a novel method of providing arefractory base with an electroconductive film of prescribed non-uniformresistance per unit square in a single spraying operation has beendiscovered. According to this method, a heated refractory base issprayed with a suitable film forming solution while maintaining a spraypattern of non-uniform density, i.e., a spray pattern which is moreconcentrated at certain portions thereof than at other portions thereof,and the spraying is discontinued after an essentially continuous filmhas been formed but before the temperature of any portion of the basefalls below minimum film forming temperature.

The spraying operation must be conducted within certain critical limitsin order that a film of non-uniform resistance per unit square can beobtained. If the spraying operation is continued too long, the amount offilm formed on all portions of the heated base tends to be uniform and afilm of substantially uniform thickness and uniform resistance per unitsquare is formed. Therefore, the complete spraying operation must beconducted within a matter of only a few seconds.

The amount of film which can be formed on the base is a function of theamount of spraying solution brought into contact with the base while thebase is at film formation temperature. Thus in order to achieve atransparent electroconductive film of non-uniform thickness andnonuniform resistance per unit area by use of a spray pattern ofnon-uniform density, the spraying must be performed within certainlimits insofar as the amount of film forming solution which is broughtinto contact with the heated base is concerned. This amount varies froman amount sufiicient to form an essentially continuous film, to anamount which is less than an amount necessary to form a maximum amountof film on all portions of the heated base. It is to be understood thatif the spraying operation is continued up to or beyond this point ofmaximum film formation, a film of substantially uniform resistance perunit area is formed. This undesirable result is accomplished becausewhile the areas of the base exposed to the dense regions of the sprayare cooled below film forming temperature, other areas of the baseexposed to the sparse regions of the spray are still above the minimumfilm forming temperature. Therefore, the film continues to form in theother areas, unless the spraying is discontinued or the exposure of thebase to the spray otherwise stopped before any area is cooled to belowminimum film forming temperature by virtue of contact with the spray.

It is known that the amount of film formation and the resistivity of thefilm are also affected by the ingredients of the spraying solution, thehumidity of the spraying atmosphere and the temperature of the base whensprayed,

but such effects are not of great importance in achieving a film ofnon-uniform resistance per unit area by a single spraying operation forthey exert the same effect on all portions of the film, thereby tendingto effect different areas of the sprayed base an equal amount.

The transparent, electroconductive films formed by such sprayingtechniques are not limited to those consisting essentially of tin oxide,as described above. Films of indium oxide, cadmium oxide, zinc oxide andother metallic oxides and mixtures of these oxides with each other andwith minor amounts of other oxides having the properties of transparencyand electroconductivity may be produced by spraying solutions of theproper metal salts or mixtures thereof on heated glass plates. Theprinciples enunciated above may be utilized to provide films containingthese other oxides and having the desired non-uniform conductivity.

FIGURE 1 is a plan view drawn to scale of a glass panel having atransparent, electroconductive coating of varying conductivity suitablefor use as a viewing closure in military aircraft;

FIGURE 2 is a diagrammatic sectional view taken along lines II-II ofFIGURE 1;

FIGURE 3 is a diagrammatic perspective view of a method of preparing aglass panel according to this invention;

FIGURE 4 is a sectional view of FIGURE 3 taken along lines IV -IV ofFIGURE 3 which run in a direction perpendicular to the path of thespray;

FIGURE 5 is a diagrammatic perspective view of another method ofpreparing a glass panel according to this invention; and

FIGURE 6 is a sectional View of FIGURE 5 taken along lines VI-VI ofFIGURE 5 which run in a direction perpendicular to the path of thespray.

The panel illustrated in FIGURE 1 comprises a glass sheet 12 ofsubstantially rectangular shape and rounded corners having bus bars orconductive edge strips 13 of an electroconductive metal such as silver,gold, etc. along opposite sides and close to the edges (preferablywithin 0.2 inch of the edge of the glass sheet). These bus bars, whichare approximately one-eighth to one inch in width, are disposed alongthe margins adjacent to the longest pair of opposite edges of the panel,whereby the distance between the bus bars is held to a minimum.Alternatively, they may be disposed on the opposite pair of shorteredges of the panel. The entire surface area between the bus bars isprovided with an electroconductive transparent film 14 of tin oxide orother material, such as is described hereinbefore.

As illustrated in FIGURE 1, the width of the glass sheet 12 is notconstant but varies from a minimum at the center to a maximum near theends thereof. Furthermore, the corners of the sheet are curved orrounded. Such rounded corners are desirable for certain structuralreasons. However, when bus bars are disposed upon such sheets, the filmadjacent the ends thereof gets too hot for plastic, sometimes crackingthe glass or burns out, particularly when the sheet is coated over itsentire area with the electroconductive coating having a uniform surfaceresistivity.

It has been found that this difficulty may be avoided to an appreciabledegree by use of bus bars which are tapered to a point at their roundedends. This taper generally begins after the change of curvature of thesheet begins and extends for a distance of about one-eighth to one ortwo inches terminating before the end of the curve. Frequently thetapered portion extends around the corner of the sheet although this isnot absolutely essential. When bars so constructed are employed, thefilm adjacent the bus bars exhibits less tendency to burn during use ofthe conductive panel.

As shown with the film greatly enlarged in FIGURE 2, theelectroconductive film 14 is thickest at the edges adjacent the bus barsand is thinnest in the central area.

6 Because of this variation in thickness, of the areas adjacent the buscentral areas.

This coating may be deposited according to the method illustrated inFIGURES 3 and 4. According to this method a glass sheet is provided withsuitable bus bars 13 by applying a thin coating of a conductingmetallizing ceramic composition such as described above.

After application of the metal bus bars to the glass sheet by paintingor other method, the sheet is heated to the temperature at whichapplication of the conductive coating may be effected, for example aboveabout 600 to 808 F. but below the fusion point of the glass, usually 950to 1250" F. During this heating operation, the ceramic metal coatingbecomes glazed and is fired onto the glass so that a firm bond isestablished between the glass and the metal coating. It is to beunderstood that certain types of metal bus bars may be applied after theelectroconductive film is applied. In such cases, the glass sheet isheated and sprayed before the application of the bus bars.

When the glass has been heated for one, two or more minutes, it iswithdrawn from the heating chamber and immediately is sprayed with thecoating solution before substantial cooling of the glass sheet can takeplace. In this operation, a quantity of the coating solution is placedin an atomizing spray gun and the heated glass sheet is sprayed with anatomized spray of this material for a brief period.

In order to obtain the film having the desired thickness variation, thespray gun is mounted and adjusted to produce a horizontally directedsplit or dumbbelP type spray which has the spray pattern illustrated bythe dots of the sectional view in FIGURE 4, being wider and more denseadjacent the spaced upper and lower end regions 15, 16 of the spraysection than in the center region 17 thereof. This spray pattern may beobtained in a conventional manner with conventional spray guns simply byusing atomizing air pressures above that required to produce a uniformspray, or by adjusting the spray :gun nozzle to widen the spray atpressures where a uniform spray is obtained.

When the spray gun has been adjusted to produce the spray patternillustrated in FIGURE 4, the glass is supported vertically and is movedtransversely through the spray with the upper and lower edges of thesheet (having bus bars 13 disposed thereon) passing horizontally throughthe upper and lower dense areas of the spray, respectively. The sheet ispassed through the spray at a rate such that a sheet approximately 26inches long in its longest dimension and having the contour illustratedin FIGURE 1 is sprayed within a matter of two to twenty seconds.Thereafter, the sheet is cooled. If necessary, in order to thicken thecoating, the glass may be reheated and resprayed.

It is to be understood of course that other procedures may be employedin spraying the base. For instance, the base may be maintainedstationary and the spray passed horizontally over the base with theupper and lower dense areas passing over the upper and lower edges ofthe base respectively. Also where a relatively small base is beingsprayed or where a large spray is being employed, the base and spray mayboth be maintained stationary. In any event, the exposure of anytransverse section of the base to the spray must end before any portionwithin the transverse section is cooled below the minimum film formingtemperature.

Various solutions may be used for this purpose. Typical suitablesolutions or mixtures are the following:

1. percent by weight SnCl .5H O

10 percent by weight aqueous formaldehyde (containing 40 percent byweight of formaldehyde). 2. 900 grams SnCI .5H O.

21 grams phenyl hydrazine hydrochloride. 9O milliliters methanol.

the conductivity bars is greater than that of 3. Anhydrous stannicchloride 20,430 grams.

Methanol 1 1,854 milliliters. Phenyl hydrazine 21 grams.

Water 7 ,056 milliliters. Dioctyl sodium sulfosuccinate solution 918grams. Such solution composed of:

Dioctyl sodium sulfosuccinate 10 grams. Methanol 45 milliliters. Water45 milliliters. 4. Solution No. 3 (without dioctyl sodiumsulfosuccinate) 70 milliliters. Aqueous formaldehyde containing 40% byweight of formaldehyde 45 grams. Ammonium bifiuoride 3 grams.

5. Solution No. 2 100 grams.

Antimony trichloride 1 or 2 grams per gram of stannic chloride in solu-Furthermore, anhydrous stannic chloride in liquid or vapor form may besprayed in this manner. In addition, other tin salts such as stannouschloride, stannic iodide, stannic fluoride as well as salts of othermetals which are capable of producing transparent electroconductivecoatings (cadmium chloride or bromide, zinc acetate or bromide, indiumtriiodide, titanium tetrachloride, etc.) may be used. I

The article thus obtained comprises a glass base or sheet with anelectroconductive film of the type described thereupon. The thickness ofthis film is diagrammatically illustrated in FIG. 2 and thus appreciablevariation in conductivity of the film may be detected.

Using a typical sheet produced according to the above process, theresistance of unit inch squares at various areas designated as A, B, C,D, E, F, G, H and I (FIGURE 1) was measured. Areas A, D, G, C, F and Iwere located within about one or two inches of the side edges, areas A,G, C and I being only about two inches from the ends of the sheet andareas D and F being about in the middle of the sheet. Areas B, E and Hwere located approximately midway between areas A and C, D and F, and Gand I respectively. The resistance per unit square in terms of ohms perunit square (the surface resistance of an area one inch'square) were asfollows:

Ohms per unit square 92 It will be understood that the resistance setforth above is the average resistance of a one inch square. Thus eventhough the resistance may have been high or even infinite at a singlepoint of minute area within the square, the resistance of the square wasas stated above. From the above table it will be apparent that the areaof maximum resistance of the film is at the zone spaced from the busbars and designated as H.

It will further be apparent that in general an area intermediate theshortest path between the bus bars at substantially any point along thebars is higher in resistance than the areas in the same path which areadjacent the bus bar. It is not necessary that the resistance in thecentral area be higher than the resistance along the entire length ofthe bus bars. It is only desired that, in determining the resistance,any shortest linear path from a point on one bus bar to the other busbar (for example from A through B to C or from D through E to F) willpass through a central area spaced from at least one of the bus bars adistance of at least 5 percent of the length of the path which is higheras to resistance per unit square than the area within 5 percent of thelength of the path (for example one inch) of the bus bar. Usually, theaverage resistance per unit square of the film within such distance froma bus bar is below the average resistance of the film.

It will be understood that wide variation in resistance over the film ispermissible. Such variation is permissible so long as the currentdistribution during passage of cur rent is such that the zones or areasof highest temperature (or current density) are spaced at least one ormore inches from the bus bar and that the temperature of the filmadjacent the bus bar is lower than that of the area of maximumtemperature or heat generation in the film.

The variation in resistance between the central area and the areasadjacent the bus bars need not be large. Thus, as shown in the abovetable, the resistance of area D is but 5 percent less than theresistance of central area E. The difference should at all events be atleast sufficient to prevent the establishment of maximum heat generationor current density in the conducting area of the film adjacent the busbar. This usually requires that the resistance per unit square (surfaceresistivity) of areas adjacent the bus bars be at least 3 to 5 percentbelow the area of maximum surface resistivity in the entire film (asmeasured in terms of unit inch squares) and preferably that the surfaceresistivity of film areas at most of the points along the bus bar be atleast 5 to 10 percent below that of the central area which is in theshortest path to the opposite bus bar. For example areas A, D and Gshould be at least 3 to 5 percent lower in resistance than the areas B,E and II respectively. In general, the average surface resistivity of astrip along the bus bar and 5 percent of the distance between the busbars in width will be lower than that of the entire sheet or at leastthat of an equal sized strip between the bus bars and spaced therefrom.Preferably the change of surface resistivity is gradual and abruptchanges normally are avoided.

A convenient method of observing and determining the location of thezone of highest heat generation on the panel involves coating theelectroconductive film with a thin coating (about 0.001 inch inthickness) of an easily fusible material such as beeswax, applying asuitable electric potential, for example l0400 volts, between the busbars and observing the point at which the wax first melts. This pointmay be considered to be the zone or area of maximum heat generation.

In certain cases it is not necessary that areas of low surfaceresistivity be adjacent both bus bars. For example, when theconfiguration of an article is such that one bus bar of two parallel busbars is substantially longer than the other, the highest current densitytends to be established adjacent the shorter bus bar. To preventexcessive heat generation, the area adjacent the shorter bus bar shouldhave lower average surface resistivity than the other area spacedtherefrom. On the other hand, the "areas along the longer bus bar do nottend to generate excessive heat, and therefore, no special precautionsmay 'be required along this bar.

Attention is called to the fact that the resistance of the areas G, Hand I are appreciably higher than the resistance in the areas on theleft side of the panel, A, B and C, or in the central areas D, E and F.This variation is established upon moving the plate or sheet through thespray, the leading edge usually having the highest resistance. Whenhigher surface resistivities are desired at one who 9 end than at theother end, they may be obtained simply by passing the panel through thespray with the end desired to have the higher surface resistivity beingthe leading edge.

In certain cases it is not necessary that the areas of low surfaceresistivity be adjacent both bus bars throughout their length. Sometimesit is desired that such areas of low surface resistivity be disposedsomewhere intermediate the bus bars. This is the case in panels having acontour such that the bus bars must be disposed in a nonparallelrelationship. A typical illustration of this type of panel is set forthin FIGURE showing a panel in the shape of a trapezoid.

In FIGURE 5 a panel 20 is shown in perspective being sprayed with ametal salt solution suitable for producing a transparentelectroconductive coating. The panel 20 comprises a glass base 22 in theform of a trapezoid having bus bars 24 disposed along the non-paralleledges of the base. If a film of uniform surface resistivity weredeposited on this glass sheet 20, there would be a tendency for thesections of the panel intermediate the closer or upper termini of thebus bars to heat up more than the rest of the panel because currentpasses more readily through the electroconductive coating where thedistance between opposed sections of the bus bars is shortest. Thisfrequently causes failures of the film adjacent the closer termini ofthe bus bars.

However, in accordance with this invention, if a film of nonuniformsurface resistivity is applied in such manner that the resistance of thefilm between the bus bars is substantially the same throughout theirlength, such failures are avoided. Such a film of non-uniform surfaceresistivity is produced on the panel 20 of FIGURE 5 by adjusting thespray gun so that an elongated spray pattern is formed such as is shownin FIGURE 6. The spray pattern is wider and more dense at the lower half23 of the pattern than at the upper half 25. This pattern may beobtained with conventional spray guns simply by adjusting the airpressure of a spra gun 26 having two air ports so that a higher airpressure is employed at one port than at the other.

The dense region 23 of the spray pattern shown in FIGURE 6 is lined upwith the areas of the glass base 22 in FIGURE 5 so that the dense regionof the spray impinges on the glass in the area where it is desired thatthe surface resistivity of the film be lowest. In the panel shown inFIGURE 5 such area is that area intermediate the termini of the bus barswhich are farthest apart, i.e., the longer edge portion 27 of the panel.In like manner, the sparse region 25 of the spray pattern is lined upwith the base so that it impinges on the base in the area where a filmof higher surface resistivity is desired. This area would be the shorteredge portion 28 between the closer termini of the bus bars in the panelin FIGURE 5, i.e., the upper portion of the panel.

The following examples illustrate the fact that the spraying operationmust be carried out within certain specified conditions in order toproduce transparent electroconductive films of non-uniform resistivity.

EXAMPLE I A series of six rectangular glass sheets 20" x 26 X wereindividually heated in a furnace at a furnace temperature of l200 F. forabout three minutes, conveyed from the furnace on a preheated horizontalconveyor, immediately sprayed with a stannic chloride solutionconsisting of the following ingredients:

The spray gun was maintained in a stationary position 10 about 14 inchesabove the glass sheet and each glass sheet was moved through the spraypath at an angle of about to the spray path at a constant conveyor speedof about 9 inches per second. By conducting the spraying in this mannerthe time that each plate was in contact with the spray was about thesame.

The air pressure on the spray gun was 62 pounds per square inch. Theamount of spraying solution striking each plate was controlled byvarying the pressure on the spraying solution flow line.

The spray pattern was in the form of a dumbbell or split spray pattern,i.e., an elongated spray pattern which is more concentrated at the endregions thereof than in the center region thereof such as shown in FIGURE 4. The sheet was passed through the spray so that the edges of thesheet which measure 26 inches in length, passed through the spaced,dense regions 15 and 16 of the elongated spray.

The resistance distribution of the transparent e1ectro conductive tinoxide films thus obtained are tabulated in Table I below together withthe corresponding spraying conditions:

Table I Surface Resistivity Amt. of 50- Solution Distribution Plate N o.lution Pressure, Ohms per square sprayed, lbs/sq. in.

grams/sec.

Top Center Bottom The resistance measurements under top and bottom weretaken about one or two inches in from edges of the glass sheet whichmeasure 26 inches in length. They were measured at areas similar tothose designated by letters D and F in FIGURE 1 near the centralportions of the edges of the sheet.

It can be seen from the results of the experiment above that in order toestablish and maintain a resistance dis tribution wherein the resistanceof the transparent electroconductive tin oxide film is greater at theedges of the film than in the center thereof, the spraying operationmust be discontinued when a certain amount of solution is applied to theglass. When larger amounts of solution are applied, the ratio of theresistance between the cen ter and edges of the glass sheet decreasesgradually to the point where a film of substantially uniform surfaceresistivity is obtained.

EXAMPLE H A further set of experiments was performed to verify theresults shown in Example I. In this set of experiments, the rate ofspeed of the conveyor was varied, thereby varying the length of time inwhich each incremental area of the plate transverse to the axis ofmovement was in the spraying zone. All other conditions were maintainedconstant.

A series of five glass sheets 20" x 26 x. were individually heated in afurnace at a furnace temperature of 1200 F. for about three minutes,conveyed from the furnace on a preheated horizontal conveyor and sprayedin the same manner as described in Example I with a stannic chloridesolution having the ingredients of the solution described in Example I.In these experiments, the rate of flow of solution was maintainedconstant, but the speed of the conveyor was varied.

The surface resistivity distributions of the transparentelectroconductive tin oxide films thus obtained are tabulated in TableII together with the corresponding spraying conditions:

It can be seen from these results that by decreasing the conveyor speed,thereby increasing the spraying time or the time wherein the glass sheetis in the spraying area, the ratio of the surface resistivity of thefilm at the center of the glass to that at the edges of the glassgradually decreases to the point where a film of substantially uniformsurface resistivity is obtained.

EXAMPLE III An approximate measure was taken of the amount of solutionstriking the various areas of a 20 X 26 x glass sheet, traveling througha spray having a dumbbell or split spray pattern at a rate of nineinches per second, when the rate of flow of spraying solution employedwas 8.67 grams per second. Three rectangular pans measuring 6 /3" acrosswere weighed and placed side by side so that their total width wasapproximately They were then passed through the spray with the edges ofthe pans which measure 20 in combined length passing through the sprayin a position parallel to the elongated spray. The amount of liquidstriking each pan was collected and the pans containing the liquid wereweighed. The outer pans collected 3.84 and 2.80 grams of solutionrespectively and the central pan collected 0.40 gram of solution. Thisgives an indication of the variation in the amount of solution strikingthe surface of a glass base when a split or dumbbell spray pattern isemployed.

EXAMPLE IV A series of three glass sheets 20" X 26 X were heatedindividually in a furnace at a furnace temperature of about 1200 F. forabout three minutes, conveyed from the furnace on a preheated horizontalconveyor and immediately sprayed with a stannic chloride solution havingthe composition disclosed in Example I.

The spraying equipment used was the same equipment as that employed inExample I. The air pressure on the spray gun was 32 pounds per squareinch and the solution pressure was about four pounds per square inch,delivering about 0.42 gram of solution per second.

The spray pattern employed was that of a round spray wherein the centralregion of the pattern is more concentrated than the edge portions of thespray. The glass sheet was passed through the spray so that the edges ofthe sheet which measure 26 inches in length passed through the lessdense or edge regions of the spray. The speed of the conveyor was variedas shown below in order that different spraying times could be employed.The circular pattern tended to produce a film which has a resistancedistribution wherein the center portion of the glass, sheet has a lowerresistance than the edges of the glass sheet. The results of suchexperiments are shown below in Table III:

Table III Oon- Surface Resistivity Distribuveyor tion, Ohms per squarePlate No. Speed,

Inches] second Top Center Bottom Spray patterns other than thosedescribed above may be used to produce transparent electroconductivefilms of non-uniform resistance per unit area. For example, the spraygun may be adjusted to form an elongated spray pattern where one endregion or the center region of the elongated pattern is moreconcentrated than the other regions of the spray. The type of spraypattern which is employed will depend upon the shape of the base uponwhich a film is to be deposited as well as the surface resistivitydistribution desired.

It can be seen from these examples that the permissible time forconducting the spraying operation while main taining a designated spraypattern, such as a dumbbell spray pattern, varies with the density ofthe spray, i.e., the total amount of solution striking the surface to besprayed. Times of from 2 to 10 seconds have been found to be suitable inthe practice of the invention. At any rate, it is generally found thatspray times of above 20 seconds are to be avoided.

The invention is particularly applicable to use in connection with thedeposition of a transparent tin oxide film. However, the invention isalso applicable in connection with tin oxide and other metal oxides incombination in the same film, such as films containing a major amount,at least '70 to percent by weight, of tin oxide with minor amounts ofthe oxides of antimony, copper, zinc, thallium, vanadium, chromium,manganese, cobalt, cadmium, indium or titanium or mixtures thereof.Furthermore, the invention is applicable with other transparentelectroconductive metal oxide films, such as cadmium oxide, zinc oxide,indium oxide, etc., which may be prepared by using the bromide, chlorideor acetate of the corresponding metal. Transparent metal oxide filmsnormally have poor light transmission but are suitable where theirproperty is not seriously objectionable.

\Vhat is claimed is:

1. In the method of providing a surface of a longitudinally extendingrefractory base with a metal oxide film formed as a heat reactionproduct of a hydrolizable metal salt, the improvement in forming a metaloxide film having a longitudinally extending thick area along alongitudinal edge portion of the base and a longitudinally extendingthin area spaced from said longitudinal edge portion, which methodcomprises heating said refractory base to a temperature of above 400 F.and below the temperature at which the base becomes molten, dispensingtoward the heated base a relatively cool spray of nonuniform density ofa composition containing a heat reactive hydrolizable metal salt capableof forming a metal oxide film upon contacting a refractory base whosetemperature is above 400 F. but incapable of forming a metal oxide filmupon contacting the refractory base when the base is at a temperaturesubstantially below 400 F., directed along a central axis thereof, saidspray being relatively dense at one region and relatively sparse atanother region, aligning the dense region of the spray with the onelongitudinal edge portion of the heated base and the sparse region ofthe spray with the area of the base spaced from the longitudinal edgeportion, establishing relative lateral movement between the heatedrefractory base and the central axis of the spray that increments of thelongitudinal edge portion of the base are exposed in succession to thedense portion of the spray and increments of the longitudinallyextending area spaced from said longitudinal edge portion of the baseare exposed in succession to the sparse region of the spray to heatreact said hydrolizable metal salt and thus form a thick metal oxidefilm on said base in each of said increments thereof exposed to thedense region of said spray and a thin metal oxide film on said base ineach of said increments thereof exposed to the sparse region of saidspray, and to cool the increments of said base exposed to the denseregion of said spray at a different rate than the increments of saidbase exposed to the sparse region of said spray are cooled, anddiscontinuing the exposure to the spray of each increment of the surfaceof the heated refractory base and heat reaction of said hydrolizablemetal salt after a period of time sufiicient to form a continuous filmof a metal oxide composition formed as the heat reaction product of saidhydrolizable metal salt thereon having a relatively thick area at thelongitudinal edge portion and a relatively thin area spaced therefrom,but before the temperature of any portion of the increment is cooled tobelow the minimum heat reaction film forming temperature.

2. In the method of providing the surface of a curved longitudinallyextending refractory base with a metal oxide film formed as a heatreaction product of a hydrolizable metal salt, the improvement informing a metal oxide film having a longitudinally extending thick areaon a longitudinal edge portion and gradually tapering in thickness fromsaid longitudinal edge portion, which method comprises heating saidrefractory base to a temperature of above 400 F. and below thetemperature at which the base becomes molten, dispensing toward theheated base a relatively cool spray of nonuniform density of acomposition containing a heat reactive hydrolizable metal salt capableof forming a metal oxide film upon contacting a refractory base whosetemperature is above 400 F. but incapable of forming a metal oxide filmupon contacting the refractory base when the base is at a temperaturesubstantially below 400 F., directed along a central axis thereof, saidspray being relatively dense at one region thereof and decreasing indensity from said dense region, aligning the dense region of the spraywith the longitudinal edge portion of the heated base and the sparseregion of the spray with a longitudinally extending area of the basespaced from the longitudinal edge portion, establishing relative lateralmovement between the heated refractory base and the central axis of thespray so that increments of the longitudinal edge portion of the baseare exposed in succession to the dense portion of the spray andincrements of the longitudinally extending area spaced from saidlongitudinal edge portion are exposed in succession to the sparse regionof the spray to heat react said hydrolizable metal salt and thus form athick metal oxide film on said base in each of the increments thereofexposed to the dense region of said spray and a thin metal oxide film onsaid base in each of the increments thereof exposed to the sparse regionof said spray and to cool the increments of said base exposed to thedense region of said spray at a different rate than the increments ofsaid base exposed to the sparse region of said spray are cooled, anddiscontinuing the exposure to the spray of each in crement of thesurface of the heated refractory base and the heat reaction of saidhydrolizable metal salt after a period of time sufficient to form acontinuous film of a metal oxide composition formed as the heat reactionproduct of said hydrolizable metal salt thereon having a relativelythick portion at the longitudinal edge portion and tapering in thicknessfrom said longitudinal edge portion, but before the temperature of anyportion of the increment is cooled to below the minimum heat reactionfilm forming temperature.

3. In the method of providing a surface of a longitudinally extendingrefractory base having non-parallel leading and trailing edges with ametal oxide film formed as a heat reaction product of a hydrolizablemetal salt, the improvement in forming a metal oxide film having alongitudinally extending thick area along the long longitudinal edgeportion and a longitudinally extending thin area along the shortlongitudinal edge portion, which method comprises heating saidrefractory base to a temperature of above 400 F. and below thetemperature at which the base becomes molten, dispensing toward theheated base a relatively cool spray of non-uniform density of acomposition containing a heat reaction bydrolizable metal salt capableof forming a metal oxide film upon contacting a refractory base whosetemperature is above 400 F. but incapable of forming a metal oxide filmupon contacting the refractory base: when the base is at a temperaturesubstantially below 400 F., directed along a central axis thereof, saidspray being relatively dense at one extremity thereof and relativelysparse at its other extremity, aligning the dense region of the spraywith the long longitudinal edge portion of the heated base and thesparse region of the spray with the short longitudinal edge portion ofthe base, establishing rela tive lateral movement between the heatedrefractory base and the central axis of the spray so that increments ofthe long longitudinal edge portion of the base are exposed in successionto the dense region of the spray and increments of the shortIon-gitudinal edge portion of the spray are exposed in succession to thesparse region of the spray to heat react said hydrolizable metal saltand thus form a thick metal oxide film on said base in each of theincrements thereof exposed to the dense region of said spray and a thinmetal oxide film on said base in each of the increments thereof exposedto the sparse region of said spray and to cool the increments of saidbase exposed to the dense region of said spray at a different rate thanthe increments of said base exposed to the sparse region of said sprayare cooled, and discontinuing the exposure to the spray of eachincrement of the surface of the heated refractory base and the heatreaction of said hydrolizable metal salt after a period of timesufiicient to form a continuous film of a metal oxide composition formedas the heat reaction product of said hydrolizable metal salt thereonhaving a relatively thick area at the long longitudinal edge portion anda relatively thin area at the short longitudinal edge portion, butbefore the temperature of any portion of the increment is cooled tobelow the minimum heat reaction, film forming temperature.

4. The method of providing a surface of a longitudinally extendingrefractory base having non-parallel leading and trailing edges with atransparent, electroconductive, metal oxide film formed as a heatreaction product of a hydrolizable metal salt, said film having alongitudinally extending thick area along the long longitudinal edgeportion and a longitudinally extending thin area along the shortlongitudinal edge portion, which method comprises heating saidrefractory base to a temperature of above 400 F. and below thetemperature at which the base becomes molten, dispensing toward theheated base a relatively cool spray of non-uniform density of acomposition containing a heat reactive hydrolizable metal salt capableof forming a transparent, electroconductive metal oxide film uponcontacting a refractory base whose temperature is above 400 F. butincapable of forming a metal oxide film upon contacting the refractorybase when the base is at a temperature substantially below 400 F.,directed along a central axis thereof, said spray being relatively denseat one extremity thereof and relatively sparse at its other extremity,aligning the dense region of the spray with the long longitudinal edgeportion of the heated base and the sparse region of the spray with theshort longitudinal edge portion of the base, establishing relativelateral movement between the heated refractory base and the central axisof the spray so that increments of the long longitudinal edge portion ofthe base are exposed in succession to the dense region of the spray andincrements of the short longitudinal edge portion of the base areexposed in succession to the sparse region of the spray to heat reactsaid hydrolizable metal salt and thus form a. thick metal oxide film onsaid base in each of the increments thereof exposed to the dense regionof said spray and a thin metal oxide film on said base in each of theincrements thereof exposed to the sparse region of said spray and tocool the increments of said base exposed to the dense region of saidspray at a different rate than the increments of said base exposed tothe sparse region of said spray are cooled, and discontinuing theexposure to the spray of each increment of the surface of the heatedrefractory base and heat reaction of said hydrolizable metal salt aftera period of time sufficient to form a continuous film of a metal oxidecomposition formed as the heat reaction product of said hydrolizablemetal salt thereon having a relatively thick area at the longerlongitudinal edge portion and a relatively thin area at the shorterlongitudinal edge portion, but before the temperature of any portion ofthe increment is cooled to below the minimum heat reaction, film formingtemperature.

5. In the method of producing a transparent electroconductive articlehaving a pair of non-parallel bus bars and a transparent,electroconductive film of non-uniform thickness in electrical contactwith the bus bars, said transparent electroconductive film formed as aheat reaction product of a hydrolizable metal salt and being thicker inthe region where the bus bars are relatively widely spaced and thin inthe region where the bus bars are most closely spaced, the improvementcomprising heating said refractory base to a temperature of above 400 F.and below the temperature at which the base becomes molten, dispensingtoward the heated base a relatively cool spray of a compositioncontaining a heat reactive hydrolizable metal salt capable of forming atransparent, electroconductive metal oxide film upon contacting arefractory base whose temperature is above 400 F. but incapable offorming a metal oxide film upon contacting the refractory base when thebase is at a temperature subsantially below 400 F., directed along acentral axis thereof, said spray being relatively dense at one extremitythereof and tapering in density to the other extremity, orienting theheated base so that one of the non-parallel edges is a leading edge andthe surface containing the bus bars is exposed to the spray, aligningthe dense region of the spray with the long longitudinal edge portion ofthe heated base extending between the non-parallel bus bars and thesparse region of the spray with the short longitudinal edge portion ofthe base extending between the non-parallel bus bars, establishingrelative lateral movement between the heated refractory base and thecentral axis of the spray so that increments of the long longitudinaledge portion of the base are exposed in succession to the dense portionof the spray and increments of the short longitudinal edge portion ofthe base are exposed in succession to the sparse region of the spray toheat react said hydrolizable metal salt and thus form a thick metaloxide film on said base in each of the increments thereof exposed to thedense region of said spray and a thin metal oxide film on said base ineach of the increments thereof exposed to the sparse region of saidspray and to cool the increments of said base exposed to the denseregion of said spray at a different rate than the increments of saidbase exposed to the sparse region of said spray are cooled, anddiscontinuing the exposure to the spray of each increment of the surfaceof the heated refractory base and the heat reaction of said hydrolizablemetal salt after a period of time suflicient to form a continuous filmof a metal oxide composition formed as the heat reaction product of saidhydrolizable metal salt having a relatively thick area at the longlongitudinal edge portion and a relatively thin area at the shortlongitudinal edge portion, but before the temperature of any portion ofthe increment is cooled to below the minimum heat reaction, film formingtemperature.

6. In the method of providing the surface of a longitudinally extendingrefractory base with a metal oxide film formed as a heat reactionproduct of a hydrolizable metal salt, the improvement in forming a metaloxide film having thick areas on said surface adjacent its longitudinaledge portions and a thin area on said surface in the intermediateportion between said longitudinal edge portions, which method comprisesheating said refractory base to a temperature above about 400 F, butbelow the temperature at which the base becomes molten, dispensingtoward the heated base a relatively cool spray of a compositioncontaining a heat reactive hydrolizable metal salt capable of forming ametal oxide film upon contacting a refractory base whose temperature isabove 400 F. but incapable of forming a metal oxide film upon contactingthe refractory base when the base is at a temperature substantiallybelow 400 F, directed along a central axis thereof, said spray beingwider and denser adjacent its extremities than in its intermediateregion, aligning the spaced dense extremities of the spray with the thespaced longitudinal edge portions of a surface of a heated base and theless dense intermediate region of the spray with the intermediateportion of the base, establishing relative lateral movement between theheated refractory base and the central axis of the spray so thatincrements of the longitudinal edge portions of the base are exposed insuccession to the extremities of the spray and increments of theintermediate portion of the base are exposed in succession to theintermediate region of the spray to heat react said hydrolizable metalsalt and thus form a thick metal oxide film on said base in each of theincrements thereof exposed to the dense region of the spray, and a thinmetal oxide film on said base in each of the increments thereof exposedto the sparse region of said spray and to cool the increments of saidbase exposed to the dense region of said spray at a dilferent rate thanthe increments of said base exposed to the sparse region of said sprayare cooled, and discontinuing the exposure to the spray of eachincrement of the surface of the heated refractory base and the heatreaction of said hydrolizable metal salt after a period of timesufficient to form a continuous film of a metal oxide composition formedas the heat reaction product of said hydrolizable metal salt havingthick areas adjacent the spaced longitudinal edge portions of the baseand a thin area in the intermediate portion of the base, but before thetemperature of any portion of the increment falls below the minimum heatreaction, film forming temperature.

7. The method of providing the surface of a longitudinally extendingrefractory base having longitudinally extending bus bars in thelongitudinal edge portions thereof with a transparent electroconductivemetal oxide film formed as a heat reaction product of a hydrolizablemetal salt, said film having thick areas in the vicinity of said busbars and a thin area on said surface intermediate said bus bars, whichmethod comprises heating the refractory base to a temperature aboveabout 400 F. but below the temperature at which the base becomes molten,dispensing toward the heated base a relatively cool spray of acomposition containing a heat reactive hydrolizable metal salt capableof forming a transparent, electroconductive metal oxide film uponcontacting a refractory base whose temperature is above 400 F. butincapable of forming a metal oxide film upon contacting the refractorybase when the base is at a temperature substantially below 400 F.,directed along a central axis thereof, said spray being wider and denseradjacent its extremities than in its intermediate region, aligning thespaced dense extremities of the spray with the spaced longitudinalextending bus bars and the intermediate region of the spray with theintermediate portion of the base, establishing relative lateral movementbetween the heated refractory base and the central axis of the spray sothat increments of the longitudinal edge portions of the base areexposed in succession to the extremities of the spray and increments ofthe intermediate longitudinal portion of the base are exposed insuccession to the intermediate region of the spray to heat react saidhydrolizable metal salt and thus form a thick metal oxide film on saidbase in each of the increments thereof exposed to the dense region ofthe spray and a thin metal oxide film on said base in each of theincrements thereof exposed to the sparse region of said spray and tocool the increments of said base exposed to the dense region of saidspray at a different rate than the increments of said base exposed tothe sparse region of said spray are cooled, and discontinuing theexposure to the spray of each increment of the surface of the heatedrefractory base and the heat reaction of said hydrolizable metal saltafter a period of time sulficient to form a continuous film of a metaloxide composition formed as the heat reaction product of saidhydrolizable metal salt having thick areas adjacent the spacedlongitudinal edge portions of the base and a thin area in theintermediate longitudinal portion of the base, but before any portion ofthe increment is cooled to below the minimum heat reaction, film formingtemperature.

8. In the method of providing a surface of a longitudinally extendingrefractory base with a metal oxide film formed as a heat reactionproduct of a hydrolizable metal salt, the improvement in forming a metaloxide film having a predetermined transverse thickness configuration andof substantially uniform thickness along any longitudinal axis thereof,which method comprises heating said refractory base to a temperatureabove 400 F. and below the temperature at which the base becomes molten,dispensing toward the heated base a relatively cool spray of acomposition containing a heat reactive hydrolizable metal salt capableof forming a metal oxide film upon contacting a refractory base whosetemperature is above 400 F. but incapable of forming a metal oxide filmupon contacting the refractory base when the base is at a temperaturesubstantially below 400 F., directed along a central axis thereof, saidspray varying in density from one extremity to its other extremityaccording to the predetermined configuration, aligning the spray alongan axis transverse to the longitudinal axis of the base, passing theheated refractory base longitudinally through the spray so thatincrements of the base along its longitudinal axis are exposed insuccession to the transverse configuration of the spray to heat reactsaid hydrolizable metal salt and thus form a metal oxide film of apredetermined thickness on said base in an increment thereof exposed toa region of said spray of a predetermined density and a metal oxide filmof a different predetermined thickness on said base in an incrementthereof exposed to a region of said spray of a different predetermineddensity and to cool an increment of said base exposed to a region ofsaid spray of a predetermined density at a rate different than anincrement of said base exposed to a region of said spray of a differentpredetermined density is cooled, removing each increment from the sprayand discontinuing the heat reaction of said hydrolizable metal saltafter a time sutficient to form a continuous film of a metal oxidecomposition formed as the heat reaction product of said hydrolizablemetal salt thereon having the desired transverse configuration butbefore the temperature of any portion of the increment is cooled tobelow the minimum heat reaction, film forming temperature.

9. The method of providing the surface of a longitudinally extendingrefractory base adapted solely for use with bus bars along thelongitudinal edges thereof with a transparent electroconductive filmformed as a heat reaction product of a hydrolizable metal salt, saidfilm having thick areas of maximum conductivity on said surface adjacentsaid bus bars and thinner areas of lower conductivity on said surface inthe central area between said bus bars to prevent establishing highcurrent densities in areas adjacent said bus bars, which methodcomprises heating said refractory base to a temperature above about 400F. but below the temperature at which the base becomes molten,establishing a relatively cool spray of a liquid containing ahydrolizable metal salt, electroconductive metal oxide film-formingcompound capable of forming a metal oxide film upon contacting arefractory base Whose temperature is above 400 F. but incapable offorming a metal oxide film upon contacting said refractory base when thebase is at a temperature substantially below 400 F directed along acentral axis thereof, said spray being wider and denser adjacent theupper and lower ends of the spray than in the central region thereofbetween said spaced denser portions of said spray, exposing the surfaceof said heated base adjacent the spaced longitudinal edges thereofadapted to engage said bus bars to the respective spaced dense portionsof said spray and the central area of said base to said less denseportion of said spray located between said spaced dense portionsthereof, establishing relative lateral movement between said heatedrefractory base and the central axis of said spray to heat react saidhydrolizable metal salt and to cool different portions of the baseexposed to different portions of the spray of different density atdifferent cooling rates, maintaining the surface of said base exposed sosaid spray transversely to and at a predetermined angle with respect tothe central axis of said spray, exposing the surface of said heatedrefractory base to said spray for a period of time suflicient to form acontinuous film of a metal oxide composition formed as the heat reactionproduct of said hydrolizable metal salt thereon having thick areasadjacent the spaced longitudinal areas of said base and thinner areas inthe central area of said base, but insufiicient for forming a film ofuniform thickness on all portions of the base and discontinuing thespray and the heat reaction of said hydrolizable metal salt before anyportion of said base is cooled below the minimum heat reaction, filmforming temperature and before a film of uniform thickness on allportions of said base is formed.

10. The method of claim 9 wherein said electroconductive film-formingcompound is a tin compound and said electroconductive film comprises tinoxide.

11. The method of claim 9 wherein said heated refractory base is movedcontinuously through said spray and said electroconductive film iscontinuously formed on the surface of said base.

12. The method of claim 9 wherein the surface of said heated refractorybody exposed to said spray is positioned substantially perpendicular tothe central axis of said spray.

13. The method of claim 9 wherein the spray is discontinued at theexpiration of a period of less than 20 seconds.

14. The method of claim 9 wherein the spray is discontinued at theexpiration of a period of from 2 to 10 seconds.

15. In the method of providing a surface of a longitudinally extendingrefractory base with a metal oxide film formed as a heat reactionproduct of a hydrolizable metal salt, the improvement in forming a metaloxide film having a longitudinally extending thick area along alongitudinal edge portion of the base and a longitudinally extendingthin area spaced from said longitudinal edge portion, which methodcomprises heating said refractory base to a temperature of above 400 F.and below the temperature at which the base becomes molten, dispensingtoward the heated base a spray of non-uniform density of a compositioncontaining a heat reactive hydrolizable metal salt capable of forming ametal oxide film upon contacting a refractory base whose temperature isabove about 400 F. and directed along a central axis thereof, said spraybeing relatively dense at one region and relatively sparse at anotherregion, aligning the dense region of the spray with the one longitudinaledge portion of the heated base and the sparse region of the spray withthe area of the base spaced from the said one longitudinal edge portion,establishing relative lateral movement between the heated refractorybase and the central axis of the spray so that the one longitudinal edgeportion of the base is exposed progressively in succession to the denseportion of the spray and the longitudinally extending area spaced fromthe one longitudinal edge portion. of the base is exposed progressivelyin succession to the sparse region of the spray to heat react saidhydrolizable metal salt and thus form a thick metal oxide film on saidbase in the portions thereof exposed to the dense region of said sprayand a thin metal oxide film on said base in the portions thereof exposedto the sparse region of said spray and to cool the portions of said baseexposed to the dense region of said spray at a different rate than theportions of said base exposed to the sparse region of said spray arecooled and discontinuing the spray on the surface of the longitudinalportions of the base exposed thereto and the heat reaction of saidhydrolizable metal salt before a film of a metal oxide compositionformed as the heat reaction product of said hydrolizable metal salt ofuniform thickness throughout said surface forms and before thetemperature of any portion of the base is cooled to below the minimumheat reaction, film forming temperature.

16. The method of claim 15 wherein the spray is dis continued at theexpiration of a period of less than 20 seconds 17. The method of claim15 wherein the spray is discontinued at the expiration of a period offrom 2 to 10 seconds.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTIUN Patent No, 3,019,135January 30, 1962 Leighton E. Orr

It is hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 3, line 43, for applied in such" read applied 15 such column 12;line 61, for "spray that" read up spray so that column 13, line 74, for"reaction" read reacti ve column 18, line 15, for "so said" read to saids Signed and sealed this 6th day of November 1962.,

(SEAL) Attest:

ERNEST w. SWIDER DAVID L MED Attesting Officer Commissioner of Patents

1. IN A METHOD OF PROVIDING A SURFACE OF A LONGITUDINALLY EXTENDINGREFRACTORY BASE WITH A METAL OXIDE FILM FORMED AS A HEAT REACTIONPRODUCT OF A HYDROLIZABLE METAL SALT, THE IMPROVEMENT IN FORMING A METALOXIDE FILM HAVING A LONGITUDINALLY EXTENDING THICK AREA ALONG ALONGITUDINAL EDGE PORTION OF THE BASE AND A LONGITUDINALLY EXTENDINGTHIN AREA SPACED FROM SAID LONGITUDINAL EDGE PORTION, WHICH METHODCOMPRISES HEATING SAID REFRACTORY BASE TO ATEMPERATURE OF ABOVE 400*F.AND BELOW THE TEMPERATURE AT WHICH THE BASE BECOMES MOLTEN, DISPENSINGTOWARD THE HEATED BASE A RELATIVELY COOLSPRAY OF NONUNIFORM DENSITY OFACOMPOSITION CONTAINING A HEAT REACTIVE HYDROLIZABLE METAL SALT CAPABLEOF FORMING A METAL OXIDE FILM UPON CONTACTING THE REFRACTORY BASE WHOSETEMPERATURE IS ABOVE 400*F. BUT INCAPABLE OF FORMING A METAL OXIDE FILMUPON CONTACTING THE REFRACTORY BASE WHEN THE BASE IS AT A TEMPERATURESUBSTANTIALLY BELOW 400*F., DIRECTED ALONG A CENTRAL AXIS THEREOF, SAIDSPRAY BEING RELATIVELY DENSE AT ONE REGION AND RELATIVELY SPARSE ATANOTHER REGION, ALIGNING THE DENSE REGION OF THE SPRAY WITH THE ONELONGITUDINAL EDGE PORTION OF THE HEATED BASE AND THE SPARSE REGION OFTHE SPRAY WEITH THE AREA OF THE BASE SPACED FROM THE LONGITUDINAL EDGEPORTION, ESTABLISHING RELATIVE LATERAL MOVEMENT BETWEEN THE HEATEDREFRACTORY BASE AND THE CENTRAL AXIS OF THE SPRAY THAT INCREMENTS OF THELONGITUDINAL EDGE PORTION OF THE BASE ARE EXPOSED IN SUCCESSION TO THEDENSE PORTION OF THE BASE SPRAY AND INCREMENTS OF THE LONGITUDNIALLYEXTENDING AREA SPACED FROM SAID LONGITUDINAL EDGE PORTION OF THE BASEARE EXPOSED IN SUCCESSION TO THE SPARSE REGION OF THE SPRAY TO HEATREACTION SAID HYDROLIZABLE METAL SALT AND THUS FORM A THICK METAL OXIDEFILM ON SAID BASE IN EACH OF SAID INCREMENTS THEREOF EXPOSED TO THEDENSE REGION OF SAID SPRAY AND A THIN METAL OXIDE FILM ON SAID BASE INEACH OF SAID INCREMENTS THEREOF EXPOSSED TO THE SPARSE REGION OF SAIDSPRAY, AND TO COOL THE INCREMENTS OF SAID BASE EXPOSED TO THE DENSEREGION OF SAID SPRAY AT A DIFFERENT RATE THAN THE INCREMENTS OF SAIDBASE EXPOSED TO THE SPARSE REGION OF SAID SPRAY ARE COOLED, ANDDISCONTINUING THE EXPOSURE TO THE SPRAY OF EACH INCREMENT OF THE SURFACEOF THE HEATED REFRACTORY BASE AND HEAT REACTION OF SAID HYDROLIZABLEMETAL SALT AFTER A PERIOD OF TIME SUFFICIENT TO FORM A CONTINUOUS FILMOF A METAL OXIDE COMPOSITION FORMED AS THE HEAT REACTION PRODUCT OF SAIDHYDROLIZABLE METAL SALT THEREON HAVING A RELATIVELY THICK AREA AT THELONGITUDINAL EDGE PORTION AND A RELATIVELY THIN AREA AT THE LONGITUDINALEDGE PORTION AND A TEMPERATURE OF ANY PORTION OF THE INCREMENT IS COOLEDTO BELOW THE MINIMUM HEAT REACTION FILM FORMINGG TEMPERATURE.